Sellafield Particle Work Programme Work Stream 3 : Transport and Dispersion Model Development Stage 1 Final Report for the Environment Agency

2 'essentially, all models are wrong, but some are useful' 'The temptation to interpret model noise as forecast information invades our living rooms every night. TV weather-forecast maps look so realistic it is hard not to over-interpret [policy makers] could help [to reduce the risk of undermining the science of climate change] by asking scientists what we know, rather than posing questions they would like answered in an ideal world.' 'Science never boils down to a choice between two alternative explanations. It is always plausible that both are wrong and a third or fourth or fifth will turn out to be correct.' A review has been completed of sediment transport processes in the offshore and littoral (beach) environments of the eastern Irish Sea, to support the Environment Agency's investigation of the causes and consequences of radioactive particles released to the environment from the Sellafield site. The study combined: a thorough literature review of published investigations (including 'grey' literature); an assessment of the availability and suitability of environmental data; a re-analysis of existing data (e.g. current meter records); a critical evaluation of hydrodynamic and sediment transport models; additional model simulations using a high resolution version of the Cefas (PRISM) model; and, a demonstration run of the XBeach beach profile model. This report presents the results of the review and a number of main conclusions and recommendations for further work, supported by a detailed analysis of the findings. The report structure is based loosely on the original set of objectives agreed with the EA. The study has provided an improved description of the geography and hydrography of the eastern Irish Sea, focussed on providing a context for better understanding the fate of 'Sellafield particles' (as identified by Sellafield Ltd.), with emphasis on those particles < 2 mm. These are more readily available for ingestion and are more amenable to modelling by conventional hydrodynamic models. This exercise highlighted a critical need for, and absence of, data describing features of the offshore and littoral environment considered important for simulating radioactive particle dispersal, such as particle burial and onshore-offshore exchange (e.g. bedform/ripple migration, cross-beach profiles, wave action in the swash zone). Some relevant data sources were identified and further investigation and analysis of these forms one of our main recommendations. We investigated the relative importance of Sellafield particle (i.e. < 2 mm) density, size and shape, from the limited data available, and concluded density and …